Evaluation of updated sepsis scoring systems and systemic inflammatory response syndrome criteria and their association with sepsis in equine neonates.

BACKGROUND: The original equine sepsis score provided a method of identifying foals with sepsis. New variables associated with sepsis have been evaluated, but the sepsis score has not been updated. OBJECTIVES: To evaluate the sensitivity and specificity of 2 updated sepsis scores and the systemic inflammatory response syndrome (SIRS) criteria in regard to detecting sepsis in foals. ANIMALS: Two-hundred and seventy-three ill foals and 25 healthy control foals. METHODS: Historical, physical examination, and clinicopathologic findings were used to calculate the original sepsis score and 2 updated sepsis scores. SIRS criteria were also evaluated. Sepsis scores and positive SIRS scores were statistically compared to foals with sepsis. RESULTS: One-hundred and twenty-six foals were septic and 147 sick-nonseptic. The original and updated sepsis scores were significantly higher in septic foals as compared to sick-nonseptic and healthy foals. The sensitivity and specificity of the updated sepsis scores to predict sepsis were not significantly better than those of the original sepsis score. One-hundred and twenty-seven of 273 (46.5%) foals met the original SIRS criteria and 88/273 (32%) foals met the equine neonatal SIRS criteria. The original SIRS criteria had similar sensitivity and specificity for predicting sepsis as did the 3 sepsis scores in our study. CONCLUSIONS AND CLINICAL IMPORTANCE: The updated sepsis scores did not provide improved ability in predicting sepsis. Fulfilling the original SIRS criteria provided similar sensitivity and specificity in predicting sepsis as the modified sepsis score and might serve as a diagnostic aid in identifying foals at risk for sepsis.

Plasma Peak and Trough Gentamicin Concentrations in Hospitalized Horses Receiving Intravenously Administered Gentamicin.

BACKGROUND: Gentamicin is an aminoglycoside antimicrobial commonly used in horses at 6.6 mg/kg IV once daily. Therapeutic drug monitoring (TDM) can confirm desired peak concentration is reached for common bacterial isolates, and detect toxicosis associated with high trough values. OBJECTIVES: Determine the relationship between gentamicin dose and plasma concentration in hospitalized horses, and identify a starting dose range to achieve peaks > 32 µg/mL. ANIMALS: Sixty-five horses (2002-2010) receiving once-daily gentamicin with TDM performed (N = 99 sets). METHODS: Retrospective study. Data from hospitalized horses including weight, dose, plasma peak, and trough gentamicin concentration, creatinine concentrations and presence of focal or systemic disease were collected from medical records. Peak concentrations measured 25-35 minutes after administration were included (N = 77). Data were divided into low (<7.7 mg/kg), medium (7.7-9.7 mg/kg) and high (>9.7 mg/kg) dose groups, and were grouped by the horse having focal or systemic disease. RESULTS: Peak concentrations resulting from doses ≥7.7 mg/kg were 5.74 µg/mL (SE 2.1 µg/mL) greater than peaks from doses <7.7 mg/kg (P = .007). Peak concentrations was 3.6 times more likely to be >32 µg/mL if dose was ≥7.7 mg/kg (P = .04). There were no significant effects of dose on trough or creatinine concentration. At a given dose, horses with focal disease had higher peaks than those with systemic disease (P = .039). CONCLUSIONS AND CLINICAL IMPORTANCE: These data suggest gentamicin dosage should be individually determined in horses using TDM, but support an initial once-daily dose of 7.7-9.7 mg/kg IV to achieve peaks >32 µg/mL and trough concentrations <2 µg/mL. Further studies evaluating the safety of doses >6.6 mg/kg are required.

Preliminary investigation of the area under the L-lactate concentration-time curve (LACArea) in critically ill equine neonates.

BACKGROUND: A variety of measures of L-lactate concentration ([LAC]) in the blood of critically ill neonatal foals have shown utility as prognostic indicators. These measures, evaluating either the severity of hyperlactatemia or the duration of exposure to hyperlactatemia, perform fairly well and have correctly classified 75-80% of foals examined in several studies. The area under the L-lactate concentration versus time curve (LACArea) encompasses both severity and duration of hyperlactatemia and should improve correct classification of patient survival. HYPOTHESIS/OBJECTIVES: LACArea is larger in nonsurviving critically ill neonatal foals. ANIMALS: Forty-nine foals admitted for critical illness to 1 of 4 referral hospitals. METHODS: Whole blood was obtained at admission and 6, 12, 18, and 24 hours after admission for measurement of L-lactate using a handheld lactate meter. LACArea was calculated for: admission-6, 6-12, 12-18, 18-24 hours, and admission-24 hours using the trapezoidal method and summing the 6-hours interval areas to determine total 24 hours area. Differences between survivors and nonsurvivors were determined using robust regression and Kruskal-Wallis testing, P < .05. RESULTS: LACArea was significantly larger in nonsurviving foals (n = 9) than in surviving foals (n = 40) at all time periods examined. CONCLUSIONS AND CLINICAL IMPORTANCE: Differences in LACArea between surviving and nonsurviving critically ill neonatal foals are large and support further investigation of this method as an improved biomarker for survival in critically ill neonatal foals is indicated.

Sequential L-lactate concentration in hospitalised equine neonates: A prospective multicentre study.

REASONS FOR PERFORMING STUDY: Evaluation of serial blood lactate concentrations [LAC] are of prognostic value for morbidity and mortality in critically ill human patients and neonatal foals, but have not been prospectively evaluated in a large multicentre study of critically ill neonatal foals. OBJECTIVES: To prospectively evaluate the prognostic value of sequential [LAC] analysis in critically ill neonatal foals with risk of mortality. STUDY DESIGN: Prospective, observational study. METHODS: Thirteen university and private equine referral hospitals enrolled 643 foals over the 2008 foaling season and [LAC] was measured at admission ([LAC]ADMIT ) and 24 ([LAC]24 ), 48 ([LAC]48 ), 72 ([LAC]72 ), 96 ([LAC]96 ) and 120 h ([LAC]120 ) after admission. [LAC] changes over time ([LAC]Δ) were calculated between sampling points. RESULTS: Nonsurvivors had significantly greater [LAC]ADMIT , [LAC]24 and [LAC]48 compared with surviving foals (P<0.001). In nonsurviving foals [LAC]Δ did not decrease over time while survivors showed significant positive [LAC]Δ between [LAC]ADM -24 and all other time periods (P<0.001). Logistic regression analysis showed that the odds of survival decreased for each 1 mmol/l [LAC] increase at all time points for all critically ill foals, independent of major final diagnoses as potential confounders. Septic foals had significantly greater [LAC] at all time points compared with nonseptic foals (P<0.001) and [LAC]Δ in septic foals was significantly more positive (suggesting better clearance of lactate from the blood) only at [LAC]ADM -24 and [LAC]72-96 (P<0.01), while in nonseptic foals [LAC]Δ was significantly positive between [LAC]ADM -24 compared with all other time periods (P<0.001). CONCLUSIONS: Blood lactate concentration is a strong, independent biomarker used to predict mortality in critically ill foals. Lactate metabolism is impaired in nonsurviving and septic foals and [LAC]Δ can be utilised to identify patients at high risk for mortality.

The effects of hyperglycemia and endotoxemia on coagulation parameters in healthy adult horses.

BACKGROUND: Hyperglycemia and endotoxemia have been associated with coagulation abnormalities in horses. Studies in humans suggest greater disturbances in coagulation with hyperglycemia and concurrent endotoxemia. OBJECTIVES: To compare coagulation parameters in horses administered with lipopolysaccharide (LPS) with and without concurrent hyperglycemia. ANIMALS: Twelve healthy adult horses. METHODS: Hyperglycemia (180-240 mg/dL) was maintained for 6 hours in 6 horses (GLU-LPS) using 140 mg/kg IV bolus of dextrose followed by a 20% dextrose constant rate infusion. A similar volume of saline was administered to an additional 6 horses (SAL-LPS). LPS (20 ng/kg) was administered to each horse. Fibrogen concentration, prothrombin time (PT), activated partial thromboplastin time (aPTT), thrombin antithrombin concentration (TAT), and thromboelastometry were measured at baseline and after 1, 1.5, 2, 2.5, 3, 4, 6, and 22 hours. Repeated measures analysis of variance was used to examine temporal changes. RESULTS: Increases in PT (P = .001) and TAT (P = .027) were observed in the GLU-LPS group. Changes in thromboelastometry parameters including increased clot formation time (In-TEM, P = .006; Ex-TEM, P = .002) and decreased alpha angle (Ex-TEM, P = .04) and maximal clot firmness (Ex-TEM, P = .014) were observed in the SAL-LPS group. Differences between SAL-LPS and GLU-LPS groups were limited to increased maximal clot firmness (Ex-TEM) at 3, 6, and 22 hours (P < .001) in the SAL-LPS group. CONCLUSIONS AND CLINICAL IMPORTANCE: Minor alterations in coagulation parameters identified for each group are most likely not clinically relevant. Observed differences between groups do not suggest that concurrent hyperglycemia and endotoxemia are associated with greater coagulation abnormalities in horses.

Association of admission L-lactate concentration in hospitalised equine neonates with presenting complaint, periparturient events, clinical diagnosis and outcome: a prospective multicentre study.

REASONS FOR PERFORMING THE STUDY: Admission L-lactate concentration is a useful and commonly measured biomarker not previously prospectively evaluated in a large multicentre study of critically ill neonatal foals. OBJECTIVES: To evaluate overall outcome and the association of survival and L-lactate concentration at admission ([LAC]ADMIT) by periparturient history, presenting complaint and clinicians' major diagnosis for ill neonatal foals. METHODS: Thirteen university and private equine referral hospitals enrolled 643 foals over the 2008 foaling season. Case details, historical, clinical and clinicopathological data were entered into standardised spreadsheets then unified for analysis. RESULTS: Overall survival was 79% (505/643). Risk of nonsurvival increased with each 1 mmol/l increase in [LAC]ADMIT (odds ratio 1.14, P < 0.001). Mean arterial pressure had a small (r2 = 19.1) but significant (P < 0.001) association with [LAC]ADMIT. Foals experiencing known dystocia or premature placental separation had increased [LAC]ADMIT (P < 0.001). Single umbilical problems (excluding uroperitoneum), meconium impaction only and failure of passive transfer of immunity only had 100% survival. Six clinicians' major diagnoses had increased odds of nonsurvival for each 1 mmol/l increase in [LAC]ADMIT: 'sepsis'; 'unspecified enterocolitis'; 'unspecified colic'; 'unspecified trauma'; 'immune related (not failure of passive transfer of immunity)' and 'respiratory only'. CONCLUSIONS AND POTENTIAL RELEVANCE: Survival of critically ill foals is good but varies with peripartum history, presenting complaint and clinicians' major diagnosis. L-lactate concentration at admission proves its utility as a valuable prognostic biomarker in neonatal foals and its utility appears to vary with peripartum history and clinicians' major diagnosis.

Sequential plasma lactate concentrations as prognostic indicators in adult equine emergencies.

BACKGROUND: Sequential lactate concentration ([LAC]) measurements have prognostic value in that hospitalized humans and neonatal foals that have a delayed return to normolactatemia have greater morbidity and case fatality rate. HYPOTHESIS: Prognosis for survival is decreased in horses with a delayed return to normal [LAC]. ANIMALS: Two hundred and fifty adult horses presented for emergency evaluation excepting horses evaluated because of only ophthalmologic conditions, superficial wounds, and septic synovitis without systemic involvement. METHODS: Prospective observational study. [LAC] was measured at admission and then at 6, 12, 24, 48, and 72 hours after admission. The change in [LAC] over time ([LAC]deltaT) was calculated from changes in [LAC] between sampling points. RESULTS: Median [LAC] was significantly (P < .001) higher at admission in nonsurvivors (4.10 mmol/L [range, 0.60-18.20 mmol/L]) when compared with survivors (1.30 mmol/L [range, 0.30-13.90 mmol/L]) and this difference remained at all subsequent time points. The odds ratio for nonsurvival increased from 1.29 (95% confidence interval 1.17-1.43) at admission to 49.90 (6.47-384) at 72 hours after admission for every 1 mmol/L increase in [LAC]. [LAC]deltaT was initially positive in all horses but became negative and significantly lower in nonsurvivors for the time periods between 24-72 hours (- 0.47, P = .001) and 48-72 hours (- 0.07, P = .032) when compared with survivors (0.00 at both time periods) consistent with lactate accumulation in nonsurvivors. CONCLUSIONS AND CLINICAL IMPORTANCE: These results indicate that lactate metabolism is impaired in critically ill horses and [LAC]deltaT can be a useful prognostic indicator in horses.

Reproducibility of airway responsiveness in horses using flowmetric plethysmography and histamine bronchoprovocation.

BACKGROUND: Inflammatory airway disease has a high prevalence in horses, but is often a diagnostic challenge. Flowmetric plethysmography and histamine bronchoprovocation (FP/HBP) is a simple and effective tool for diagnosis, but reproducibility of these measurements made over time has not been established. HYPOTHESIS: We hypothesize that the measurement of airway responsiveness in horses using FP/HBP is consistent over both short and long periods of time. ANIMALS: Twenty-nine healthy adult horses from 2 university herds. METHODS: In this prospective experimental study, airway responsiveness was determined in each horse at day 0 (baseline [BL]) with FP/ HBP, using PC35 (provocative concentration of histamine needed to increase Delta(flow) by 35%) as a measure of airway responsiveness. Each horse was re-tested 1-4 weeks after BL (short-term [ST]) and again at 3-12 months after BL (long-term [LT]). RESULTS: In the ST period, 23/27 (85%) of the horses had a PC35 that was within 1 doubling concentration of histamine of their BL value, with a mean change of 0.52 doubling concentrations (95% CI 0.26-0.79, range 0-2.06). For the LT data, 19/26 (73%) of horses were within 1 doubling concentration of their BL value, with a mean change of 0.81 doubling concentrations (95% CI 0.45-1.17, range 0.14-3.10). There was no significant difference in reproducibility between the 2 groups of subjects. CONCLUSIONS AND CLINICAL IMPORTANCE: Repeated measurements of airway responsiveness obtained with FP/HBP show acceptable reproducibility over time periods up to a year. However, caution must be used when testing horses when ambient air temperature is low.

Association of blood lactate concentration and outcome in foals.

BACKGROUND: Lactate concentration in blood or plasma ([LAC]) and change in [LAC] are associated with survival in sick foals. HYPOTHESIS: [LAC] and change in [LAC] over time are associated with survival at 96 hours and discharge in neonatal foals. Furthermore [LAC] and change in [LAC] over time correlate with blood culture results and blood pressure at admission. ANIMALS: Two hundred and twenty-five foals consecutively admitted to a Neonatal Intensive Care Unit. METHODS: Retrospective case review. Foals

Prospective evaluation of coagulation in critically ill neonatal foals.

BACKGROUND: Coagulopathy is a potentially underrecognized complication of sepsis and septic shock in critically ill neonatal foals. HYPOTHESIS: Critically ill neonatal foals have abnormalities in coagulation that are associated with disease severity and outcome. ANIMALS: Foals <72 hours old admitted to a neonatal intensive care unit. METHODS: Prospective, observational study. Blood was collected at admission, 24, and 48 hours for platelet count, prothrombin time, activated partial thromboplastin time, antithrombin activity and concentrations of fibrin degradation products, and fibrinogen in plasma from all foals. RESULTS: Sixty-three foals were enrolled and classified as Septic Shock (12), Septic (28), and Other (23). At least 1 abnormal value was found in 18/28 (64%) samples from the Septic Shock group, 66/85 (78%) from the Septic group, and 30/59 (51%) from the Other group (P= .01). Coagulopathy (3 or more abnormal values) was present in 7/28 (25%) samples in the Septic Shock group, 14/85 (16%) samples in the Septic group, and 3/59 (5%) samples in the Other group (P= .0028). Clinically detectable bleeding occurred in 8/12 (67%) Septic Shock cases, 11/28 (39%) Septic cases, and 3/23 (13%) Other cases (P= .009). Foals in Septic Shock were 12.7 times more likely to have clinical evidence of bleeding than those in the Other group (95% CI 2.3-70, P= .004). Treatment with fluids or plasma did not have a detectable effect on coagulation values. CONCLUSIONS AND CLINICAL IMPORTANCE: Coagulopathy commonly occurs in critically ill neonatal foals, especially those with sepsis and septic shock.

Bacteremia in equine neonatal diarrhea: a retrospective study (1990-2007).

BACKGROUND: Bacteremia in sick foals is associated with survival, but the association of bacteremia and diarrhea is not reported. HYPOTHESIS: Neonatal foals with diarrhea will commonly be bacteremic. ANIMALS: One hundred and thirty-three neonatal foals. METHODS: Records of all foals <30 days of age presenting with diarrhea between January 1990 and September 2007 were reviewed. RESULTS: Sixty-six of 133 foals (50%) were bacteremic at admission, with 75 isolates from the 66 samples. The blood culture from a further 18 foals (13.5%) grew coryneform bacteria. Nine foals (6.8%) had 2 or more organisms grown on blood culture. One foal had 5 different organisms, interpreted as contamination. Forty-eight foals (36%) had no growth on admission blood cultures. No cultures isolated fungal organisms. Excluding coryneform bacteria, 43 isolates (57%) were Gram-negative organisms and 32 isolates (43%) were Gram-positive organisms. The most common isolate was Enterococcus spp. (22 isolates, 29%), followed by Pantoea agglomerans (13 isolates, 17%). IgG concentration at admission was not associated with blood culture status. Blood culture status was not associated with survival to hospital discharge. CONCLUSIONS AND CLINICAL IMPORTANCE: Bacteremia is common in neonatal foals with diarrhea. Decisions regarding antimicrobial selection should be made with these differences in mind.

Comparison of the Accu-Chek Aviva point-of-care glucometer with blood gas and laboratory methods of analysis of glucose measurement in equine emergency patients.

BACKGROUND: More information is needed regarding accuracy of commonly used methods of glucose measurement in the critically ill horse. HYPOTHESIS: Glucometry will have good agreement with a laboratory standard. Glucometry with plasma will have better agreement than when performed with whole blood. ANIMALS: Fifty sequentially admitted equine emergency patients, aged >1year. METHODS: Venous blood was collected at admission and immediately analyzed by point-of-care glucometry on both whole blood (POC/WB) and plasma (POC/PL), a multielectrode blood gas analyzer with whole blood (BLG), and a standard laboratory method with plasma (CHEM). Paired data were compared using Lin's concordance correlation, Pearson's correlation, and robust regression. Bias and limits of agreement were tested by the Bland-Altman technique. Bivariate regression analysis was used to explore confounding factors. RESULTS: Concordance was significant for all comparisons, and was strongest for CHEM-POC/PL (0.977) and weakest for POC/WB-POC/PL (0.668). Pearson's correlation was excellent for all comparisons except those with POC/WB. All comparisons had excellent robust regression coefficients except those with POC/WB. CONCLUSIONS AND CLINICAL IMPORTANCE: POC glucometry with plasma had excellent agreement with a laboratory standard, as did blood gas analysis. POC glucometry with whole blood correlated poorly with a laboratory standard. These differences may be clinically important, and could affect decisions based on glucose concentrations.

Hepatic encephalopathy in a pregnant mare: identification of histopathological changes in the brain of a mare and fetus.

An 11-year-old Thoroughbred broodmare was evaluated for suspected hepatic dysfunction. Clinical signs of hepatic encephalopathy were evident at admission. Hepatic ultrasonographic evaluation revealed an increase in hepatic size, rounded borders and normal echogenicity. There was no evidence of cholelithiasis or bile duct distention. Increased activity of hepatic enzymes, increased bile acid and bilirubin concentration and an increased ammonia concentration were supportive of a diagnosis of hepatic disease and hepatic encephalopathy. Histopathological evaluation of a liver biopsy specimen was consistent with chronic active hepatitis. The mare was treated with intravenous fluids and antimicrobials, pentoxyfilline, branched-chain amino acids and dietary manipulation. Clinical improvement was observed initially; however, 3 weeks later, deterioration in the mare's condition necessitated euthanasia. Pathological lesions at necropsy were restricted to the liver and brain. The liver was diffusely firm with a prominent reticular pattern on the cut surface. A large choledocholith was present in the main bile duct of the left liver lobe. Histopathological examination of the liver revealed severe fibrosis, with hyperplastic bile ducts and mononuclear and neutrophilic inflammation. Pathological changes consistent with hepatic encephalopathy, (Alzheimer type II cells), were evident in the cerebrum of both the mare and the fetus.

Retrospective study of dystocia in mares at a referral hospital.

REASONS FOR PERFORMING STUDY: The period between the onset of dystocia and its resolution has an important bearing on fetal outcome. There are few published data on which to base decisions regarding optimum management of cases in practice. OBJECTIVES: To evaluate and compare the effects of a coordinated dystocia management protocol (CDMP) with that of a previous protocol of random management on time to resolution and outcome in both an emergency dystocia referral population of mares (referred emergency cases: EM) and in a population of mares residing in hospital due to high risk pregnancy (HRP) concerns that then experience dystocia at parturition. METHODS: Retrospective study performed at a university hospital referral centre of cases presenting from 1991-2004 divided into Group 1 (pre-CDMP) and Group 2 (CDMP). RESULTS: Medical records of 71 cases with dystocia were retrieved and data recorded. For referred emergency cases (EM), time from hospital presentation to resolution decreased significantly by 32 min (P = 0.03) after institution of CDMP. Survival rate of mares at discharge was 86%. Survival of EM foals was low, with 10% in Group 1 and 13% in Group 2, surviving to discharge. For EM foals delivered alive, survival to discharge was 30% and 43% in Groups 1 and 2, respectively. Median Stage II was significantly (P < 0.001) different at 71 and 282 min for EM foals delivered alive vs. those not alive at delivery, respectively. Median duration of Stage II was also significantly (P < 0.001) different between EM foals surviving and not surviving to discharge, at 44 and 249 min, respectively. Survival of HRP dystocia foals to discharge was 79%. CONCLUSIONS: Although CDMP reduced the time from presentation at the hospital to resolution significantly for EM, total duration of Stage II for EM was unchanged, as was foal outcome. POTENTIAL RELEVANCE: Very early referral of mares with dystocia to referral centres with dystocia management protocols may improve fetal outcome as increased duration of Stage II in the horse affects fetal outcome negatively.

Congenital cystic polypoid rectal hamartoma in a newborn foal.

A neonatal foal with signs of rectal bleeding was diagnosed with an intraluminal rectal mass and intussusception on surgical exploration of the abdomen. Histologically, the mass consisted of cystic spaces lined by simple columnar epithelium with numerous goblet cells and was surrounded by thin bands of smooth muscle in a myxomatous stroma. Although the mass shared similarities with retrorectal cystic hamartoma (tailgut cyst) and juvenile polyps, described in human medicine, location and histologic findings were not entirely consistent with either condition.

Extravascular lung water in the exercising horse.

Seven Standardbred horses were exercised on a treadmill at speeds (approximately 12 m/s) producing maximal heart rate, hypoxemia, and a mean pulmonary arterial pressure of approximately 75 mmHg. Extravascular lung water was measured by using transients in temperature and electrical impedance of the blood caused by a bolus injection of cold saline solution. Lung water was approximately 3 ml/kg body wt when standing but did not increase significantly with exertion. We conclude that any increase in fluid extravasation from the pulmonary hypertension accumulates in the lung at a level that is less than that detectable by this method. At maximal exertion, the volume of blood measured between the jugular vein and the carotid artery increased by approximately 8 ml/kg, and the actively circulating component of the systemic blood volume increased by approximately 17 ml/kg with respect to corresponding values obtained when walking before exertion. These volume increases, reflecting recruitment and dilatation of capillaries, increase the area for respiratory gas exchange and offset the reduced transit times that would otherwise be imposed by the approximately eightfold increase in cardiac output at maximal exertion.

Clinical, pathologic, immunohistochemical, and virologic findings of eastern equine encephalomyelitis in two horses.

Natural eastern equine encephalitis alphavirus (EEEV) infection was diagnosed in two adult horses with anorexia and colic, changes in sensorium, hyperexcitability, and terminal severe depression. Myocardium, tunica muscularis of stomach, intestine, urinary bladder, and spleen capsule had coagulative necrosis and perivascular lymphocytic infiltrate. Central nervous system (CNS) lesions were diffuse polioencephalomyelitis with leptomeningitis characterized by perivascular T lymphocyte cuffing, marked gliosis, neuronophagia, and multifocal microabscesses. Lesions were more prominent within cerebral cortex, thalamus, hypothalamus, and mesencephalon. EEEV was identified in the cytoplasm of cardiac myocytes and smooth muscle cells of spleen, stomach, intestine, urinary bladder, blood vessels, and dendritic cells. In the CNS, EEEV-positive cells included neurons, astrocytes, oligodendrocytes, microglia, and neutrophils. EEEV was isolated from the CNS of both horses. The detailed description of the encephalic and spinal EEEV localization and the findings of EEEV in extraneural tissues contribute to the understanding of this important multisystemic zoonotic disease.